1. Technical Field of the Invention
The present invention relates to a digital audio device and a method of operating the same appropriate for use in PA equipment such as an amplifier for concerts.
2. Description of the Related Art
Digitization of audio devices used for concerts or the like, which will also be referred to as PA equipment, is in progress. Specifically, a system has been commercialized, in which, although audio signals output from a mixer are output through an amplifier and a speaker, a range of components from the mixer to input terminals of the amplifier are all digital and the digital audio signals are amplified after conversion into analog signals in the amplifier, and the amplified audio signals are then emitted through the speaker. Signals input to such an amplifier that receives digital audio signals, which is referred to as a “digital amplifier”, generally employ formats such as AES/EBU and ADAT. These formats enable two audio signals to be transmitted through one twisted pair cable and also enable one clock signal to be superimposed in the audio signals.
In this specification, a connector or the like corresponding to one twisted pair cable is referred to as an “input port”. For example, a 3-pin XLR connector or the like is used as the input port. Accordingly, 4 input ports may be provided for an 8-channel digital amplifier. For the digital amplifier, there is a need to define a clock signal for use as a reference signal for operations of the channels. This clock signal is referred to as a “word clock”. Although some digital amplifiers have a terminal dedicated to receiving the word clock, many types of digital amplifiers do not have such a dedicated terminal. For such types of digital amplifiers, there is a need to select a particular input port for receiving the word clock from among a plurality of input ports.
Japanese Patent Application Publication No. 9-9399 describes a technology for selecting an input port for receiving a word clock in PA equipment. Although Japanese Patent Application Publication No. 9-9399 directly describes a “mixer” as an embodiment, the technology described therein is also applicable to other PA equipment such as a digital amplifier. Specifically, in Japanese Patent Application Publication No. 9-9399, each input port that receives a clock signal that may be used as a word clock and each input port that receives no clock signal among a plurality of input ports provided on the mixer are displayed so as to be discriminated from each other on a display. Then, using a specific control piece or the like, the user can select one of the input ports which receive clock signals as an input port for receiving a word clock.
However, in a relatively wide concert venue (for example, a baseball field), a great number of digital amplifiers are installed at separate locations. It is very troublesome to individually set a port for receiving a word clock for each of the digital amplifiers using the technology of Japanese Patent Application Publication No. 9-9399. If a wrong word clock supply source is selected for a digital amplifier, the digital amplifier outputs no audio signal. Since analog amplifiers that receive audio signals are free from this problem, it takes a long time for users who are accustomed to working with analog amplifiers to determine the cause of the problem.
Due to these circumstances, from the viewpoint of the user, there has been demand for a digital amplifier that can be operated simply by connecting a cable for input signals to the digital mixer, similar to the analog amplifier.